1. Field of the Invention
The present invention relates to an etching apparatus for manufacturing semiconductor devices, and more particularly, to an etching apparatus which reduces contamination of the surface of wafers during the step of transporting wafers to a process chamber and the step of etching the wafer as well as reducing the time it takes to transport and etch the wafers.
2. Discussion of Related Art
The manufacture of semiconductor devices involves many processes, including photolithography, etching, and thin film fabrication, which are repeatedly performed during the manufacturing process. The etching process is required to eliminate any unnecessary film on the wafer, and can be divided into wet-etching processes utilizing chemicals, and dry-etching processes utilizing plasma.
FIGS. 1 and 2 schematically illustrate the structure of a conventional dry-etching apparatus. The conventional dry-etching apparatus has multiple process chambers 1; a load lock chamber 3 disposed between the process chamber 1 and the wafer supply mechanism part 2 which supplies wafers W to the vacuum process chamber 1 with the processing surface of the wafers facing up; and an aligner 4 for aligning a flat edge of the wafer W so that the wafers W are aligned before they are supplied to process chamber 1.
In the conventional apparatus, process chamber 1 has a cathode 5 on which the wafer W is laid with the processing surface of the wafer facing upward. The gas supply diffuser 11 supplies a process gas to process chamber 1 wherein the gas immediately forms a plasma that etches the upward-facing processing surface of the wafer. The inside of processing chamber 1 is maintained under a strong vacuum to assure a stable etching process.
Inside load lock chamber 3, there is an elevator 6 and a robot 7. The arm 12 of the robot 7 loads wafers from cassette 8 of the wafer supply mechanism 2 onto elevator 6, where the wafers W are stacked. The arm 12 of robot 7 takes one wafer W at a time from the elevator 6 as arm 12 moves up and down to align the wafer through the aligner 4. Arm 12 then transports wafer W to process chamber 1 where the etching step takes place. After etching, the wafer W is loaded in wafer block 9 on the elevator 6 and is returned to the wafer supply mechanism 2.
Transporting wafers W from the wafer supply mechanism 2 to the process chamber 1 is a slow process. First, the wafers W stacked in the cassette 8 of the wafer supply mechanism 2 are transported one by one, and sequentially inserted into the wafer block 9 of the load lock chamber 3. The wafer supply mechanism 2 has a table 10 on which at least one cassette 8 is laid. The table 10 moves horizontally to the left and right, and thus allows for a continuous supply of wafers W stacked in multiple cassettes 8. The wafers W in the wafer block 9 are then transported one by one to the aligner 4 where their flat edges are aligned. After aligning, the wafers W are transported one at a time with the processing surface facing upward to the process chamber 1 where they are etched. In the conventional apparatus, the wafers are transported and aligned individually which is slow and inefficient, resulting in decreased productivity.
The wafer supply mechanism 2 is maintained under atmospheric conditions, while the process chamber 1 is maintained under a strong vacuum to facilitate the plasma etching step. When the wafers W are transported to the wafer block 9 inside the load lock chamber 3 from the wafer supply mechanism 2, care must be taken to maintain the path to the process chamber 1 from the load lock chamber 3 in the high vacuum state. To accomplish this, load lock chamber 3 is maintained under atmospheric conditions while the wafer W is transported from wafer supply mechanism 2 to load lock chamber 3. Before transporting the wafer W from the load lock chamber 3 to the process chamber 1, the path between the load lock chamber and the wafer supply mechanism 2 is closed. The path between load lock chamber 3 and process chamber 1 is then opened so that the load lock chamber 3 can be put under a high vacuum thereby reducing the pressure difference between load lock chamber 3 and process chamber 1.
Contamination of the surface of the wafer W causes failures in the etching process. Therefore, it is important that the inside of the load lock chamber 3 and the process chamber 1 be clean. It is also necessary that the apparatus itself be placed in a clean environment to effectively prevent contamination of the wafer and the chambers of the apparatus.
There is a high risk of contamination of the upward-facing processing surface of the wafers W from particles that become attached to the surface as the wafers W are transported from the wafer supplying part 2 through load lock chamber 9 to the process chamber 1 where they are etched. Therefore, a need exists for an etching apparatus for manufacturing semiconductor devices that is faster and more efficient, and that reduces particle contamination of the wafer surface.
An objective of the present invention is to provide an etching apparatus for manufacturing semiconductor devices which reduces contamination of the processing surface of the wafers caused by environmental contaminants while the wafer is transported back and forth between the wafer supply mechanism and the process chamber where the wafer is etched.
It is another aspect of the present invention to reduce the process time required to transport the wafers back and forth between the wafer supply mechanism and the process chamber where the wafer is etched, and the time required to align the flat edges of the wafers, thereby enhancing operational efficiency of the etching apparatus.
To achieve these and other advantages, the present invention provides an etching apparatus for manufacturing semiconductor devices, having one or more process chambers for etching a wafer with the processing surface facing down during the etching step. The apparatus has a cassette supply chamber for supplying a plurality of wafers to the process chamber, and the cassette supplying chamber has a cassette supply table for receiving a cassette housing a plurality of wafers stacked in the cassette with their processing surfaces facing down. A load lock chamber is provided for transferring the wafers housed in the cassette from the cassette supply chamber which is maintained under atmospheric conditions, to the process chamber which is maintained under a strong vacuum, the load lock chamber being installed between the process chamber and the cassette supply chamber, and having an elevator for moving the cassette up and down. The load lock chamber also has a wafer transporting mechanism for transferring the wafers from the cassette to the process chamber one by one while maintaining the orientation of each wafer with the processing surface facing down; and a cassette transport mechanism for transferring the cassette from the cassette supply table in the cassette supply chamber to the elevator in the load lock chamber.
In a preferred embodiment, the process chamber encompasses a sealed volume and has a side opening in communication with the load lock chamber which opening is sealed by a door, and a removable lower cover for easy cleaning and repair. The process chamber also has a cathode installed in the top part inside the chamber body, onto which cathode the wafer is clamped with its processing surface facing down to minimize contamination of the surface of the wafer during transport to and from the process chamber and during etching. The process chamber has a wafer loading mechanism for receiving the wafer supplied to the process chamber from the load lock chamber, and for clamping the wafer against the cathode. Finally, the process chamber has a process gas supplying component installed in the bottom of the chamber body for supplying the process gas to the chamber for etching the downward-facing wafer processing surface.
In a preferred embodiment, the wafer loading mechanism has a wafer loader for loading the wafer onto the cathode and a wafer holder for clamping the wafer onto the cathode. The positions of the wafer loader and the wafer holder are determined by sensors. In another aspect of the present invention, the wafer loader and the wafer holder are moved up and down inside the process chamber by a driving means that is driven by pneumatic pressure.
In a preferred embodiment, the etching apparatus has a process gas supply component, comprising a gas spray plate having a plurality of gas orifices that is installed in the bottom of the chamber body at an interval above the lower cover. Process gas is supplied by a gas supply line that passes through the lower sidewall of the process chamber body with one end of the line passing through the gas spray plate and terminating at a point between the gas spray plate and the lower cover, thereby supplying process gas to the space between the gas spray plate and the lower cover.
In another aspect of the invention, the cassette supply chamber has a cassette supply table that has multiple fixing tables stacked at a predetermined interval from each other for receiving a cassette. The fixing tables have pneumatically driven clamping bars to fix and hold the cassette, and they can move up and down depending on the direction of rotation of a ball screw that is driven by a motor.
In another preferred embodiment, the etching apparatus of the present invention has a wafer aligning chamber containing a wafer aligning mechanism installed between the cassette supply chamber and the load lock chamber for simultaneously aligning the multiple wafers stacked in the cassette, and for transferring the cassette to the load lock chamber.